1. Field of the Invention
The present invention relates to a pattern generation circuit, a multi-path detection circuit employing the same and a multi-path detection method. More particularly, the invention relates to a detection method of a multi-path position for determining a reception timing of a finger of a RAKE receiver employed in a code division multiple access (CDMA) system (spread spectrum system).
2. Description of the Related Art
Conventionally, as a path timing detection circuit of this kind, there is a circuit to be realized by measuring a delay profile of a propagation path by correlating operation of a reception signal and a spread code using a sliding correlator or matched filter and by detecting a correlation peak amount of the delay profile.
However, when intervals of respective multi-path is narrow, a plurality of paths can overlap on the delay profile to make it difficult to detect correct path position.
For example, in an example of the delay profile shown in FIGS. 5A to 5C, when only one path is present, a shape of the path has a width as illustrated in FIG. 5A. On the other hand, when a plurality of paths are present, if paths have enough interval as shown in FIG. 5B, a plurality of paths can be identified.
However, when interval of the paths is small as shown in FIG. 5C, paths cause overlap to make it impossible to identify which sample point is the accurate path position. When the path position cannot be detected accurately, reception performance is degraded significantly.
In such case, in the prior art, it has been employed a method to set a minimum interval of respective finger position by omitting N samples (N is integer) before and after the detected path from next peak detection. Such method has been disclosed in “Path-Search Performance of DS-CDMA System in Laboratory and Field Experiments” (Aoyama et al.: Technical Report of IEICE, ROS 97–164, 1997–11) (hereinafter referred to as publication 1).
However, in the foregoing method, it is required to preliminarily determine the minimum interval of the paths to detect. Also, in the foregoing method, the detected path position may be determined depending upon the set value to cause difficulty in detecting accurate timing.
Namely, in the foregoing publication 1, when the interval between the paths is narrow to overlap the paths, the N samples before and after the detected path are masked to omit from next peak detection, pseudo peak may appear in the pattern from which the N samples before and after the detected path are omitted, to cause difficult in detection of the accurate timing.